1. Field of the Invention
The present invention relates to an optical system, and in particular to a Head Up Display (HUD) suitable for use in a moving vehicle.
2. The Prior Arts
It is well known that the Head Up Display (HUD) is an auxiliary aviation instrument that is first utilized in an aircraft, so that a pilot is able to look at the information on the panel without lowering his head, to avoid interruption of attention and lose Situation Awareness. The Head Up Display (HUD) can not only provide convenience in usage, but it can also raise the aviation safety. Therefore, it can be used in any types of the moving vehicles, such as aircrafts, or even automobiles and ships.
In the past, the Head Up Display of the prior art could provide only a small display area of simple instrument information within the eyesight of the driver, to indicate the critical information related to the moving vehicle. For the Head Up Displays (HUD) of the prior art, most of them belong to a single optical-route display device having only a small display area, and that is realized through the following ways. Firstly, the critical information is projected onto an optical device, and the display screen is placed inside the wind shield and facing the wind shield, so that the critical information is transmitted to the display screen through the optical device. Then, the critical information displayed on the display screen is reflected by the wind shield and displayed on the wind shield. Also, the position of display is in the eyesight directly in front of the driver, so that in driving a vehicle, the driver is able to view directly the vehicle driving speed or other data he desires to know, without the need to raise or lower his head to change his eyesight. However, according to the optical imaging principle of such a single optical-route display device, for any lens or mirrors utilized, the imaging area of the input image is positively proportional to the size of lenses and mirrors. As such, a Head Up Display requires an enormously large lens or mirror to project out virtual images, thus it is not easy to integrate such a single optical-route display device with an instrument panel into an integral unit, since the volume required by such a Head Up Display would be too large for the panel full of wires and connections. In addition, in order to keep the quality of imaging, the size of optical elements used for a Head Up Display can not be reduced further, therefore, it is rather difficult to achieve large display area in a very limited space of the driver cabin. Also, for the information displayed in an overly small display area, the driver is not able to obtain critical information right away by just glancing briefly over instrument control panel. Or, in case that the driver does raise his head to look at and get the critical information on the display panel in detail, that could disrupt his attention and put him in an immediate danger.
Therefore, presently, the design and performance of the Head Up Display (HUD) is not quite satisfactory, and it has much room for improvements.